1. Field of the Invention
The present invention relates to a bump bonding apparatus for forming, by means of a wire bonding technique, bumps for establishing an electrical connection to an electrode part of an IC chip. More specifically, the present invention relates to a bump bonding apparatus and method for forming such bumps on the wafer before being cut into IC chips.
2. Description of Related Art
Demand for smaller and lighter electronic devices has accelerated in recent years, particularly with respect to portable devices, and this has significantly increased demand for smaller IC chips for use in these electronic devices.
Conventionally, in a bump bonding apparatus, a single wafer is diced into a plurality of individual IC chips, and each IC chip is transported and positioned onto the bonding stage for bonding by ones, to form bumps at the electrode parts on the IC chip. Such bump bonding apparatuses, however, suffer from numerous technical problems, including: low production efficiency; difficulty in moving and handling the IC chips with a tray; and difficulty in positioning the IC chips with good precision.
Some of these problems can be addressed by forming bumps for individual IC chips before dicing the wafers into individual chips.
As described more fully below, however, forming bumps directly onto the undiced wafer presents a different set of technical difficulties as compared with handling the individual IC chips, and these problems must therefore be resolved in practice.
For example, while the wafers supplied to the bump bonding apparatus are stacked on multiple shelves in the wafer carrier, the wafers are loose in the carrier. Therefore, after the wafers are extracted from the carrier and regulated for their position on the positioning table, these wafers are moved to the bonding stage. The wafers are circular discs having a straight orientation flat cut into one edge of the wafer. On the positioning table, it is necessary to regulate a center of the wafer in position and regulate the circumferential location of the orientation flat. This requires a complex mechanism, such as a turntable and means for positioning the wafer from four directions around the wafer circumference. Positioning is also time consuming. Because the wafers are loose in the carrier, there is also the further danger of carrier vibration causing a wafer to fall out from its storage location.
When bumps are formed at various points around the entire surface of the stationary wafer with a large area, the relative movement distance of the bonding head and bonding stage becomes rather long. Therefore, a longer arm is required for the bonding mechanism. This makes it mechanically difficult to assure sufficient positioning precision. These problems can be addressed by dividing the wafer circumferentially into a plurality of segments for bump formation, turning the wafer about its center when all bumps in one segment are formed, positioning the next segment for bump formation, and then forming the bumps in that segment.
In such a case, if the bonding stage, on which the wafer is fixed, is turned, it heats up the stage. Thus, thermal expansion and contraction of the turn drive mechanism makes consistent, high precision positioning difficult. This heat problem can be addressed in part by blowing a turn air flow to the bottom of the wafer to float and turn the wafer, and stopping the turn of the wafer based either on a timer or visual inspection by an operator. A problem with this method, however, is that minute variations in the turning air flow cause the wafer to move irregularly, easily producing variations in rotational positioning. Therefore, consistent, stable wafer positioning is difficult with the method.
Through extensive research focused on the various technical problems presented by directly forming bumps on an IC wafer before wafer dicing, the inventors of the present invention proposed, in Japanese Patent application No. 3-323064, a bump bonding apparatus and bump forming method that effectively resolves the above-noted problems.
However, while the above-noted bump bonding apparatus and bump forming method effectively solves the conventional problems described above, there remain a number of technical problems to be solved in order to yet further improve productivity, reduce cost, and improve quality.
With a conventional bump bonding apparatus, for example, the wafers are stored and supplied to the bump bonding apparatus in a stack on a plurality of shelves formed in the carrier. To make positioning the wafers on the bonding stage easier, a position regulating means is provided on the extractor for extracting the wafers from the carrier. A four-points, chuck holds the wafer at four points after regulating the orientation flat to be oriented in a specific direction using the position regulating means, and moves the wafer to the bonding stage. Inserting the wafers in the carrier is a manual task performed by the operator. The operator must carefully insert each wafer in the carrier with the orientation flat oriented in a specific direction, so that the later positioning operation can proceed smoothly.
This means that the operator may need to repeatedly handle a wafer in order to position the orientation flat properly. In addition to making the operator work greater, this also increases the potential for damage to high cost wafers. Further, in such a case, the wafer is regulated for its position before being transported to the bonding stage. This also increases the number of times for wafer handling, and thus increases the potential for wafer damage.
Also further, when the chuck holds the wafer at several points around the edge of the wafer for transport, it is also possible for one of the chucking points to be on the orientation flat of the wafer. If the chuck holds the wafer at only a few points, such as four points in the case of a 4-chucking points type chuck, the wafer may not be properly centered in the chuck. This means that despite efforts to regulate the wafer for its position, the orientation flat may become out of position, while the wafer is transported onto the bonding stage.
A sensor provided on the bonding stage is also used to detect the position of the orientation flat on the boding stage in a conventional bump bonding apparatus. The bonding stage typically reaches temperatures of approximately 300 degrees centigrade. Therefore, expensive heat resistant sensors capable of withstanding such temperatures must be used for the orientation flat sensor, and this contributes to higher cost.
A conventional bump bonding apparatus also typically has an orientation flat sensor located on only one side of the bonding stage. This makes wafer positioning difficult when the wafer is divided circumferentially into plural segments for bump formation, and the wafer is sequentially turned about its center to form bumps in one section at a time. The air blowing means that is used for pushing the wafer to one side is also provided only in one direction, on which the orientation flat sensor is mounted. Furthermore, while only one orientation flat sensor is provided, a plurality of sensors is preferably provided along the base line of the orientation flat (the cut edge on the outside edge of the wafer) to improve the precision for detecting the orientation flat.
As also noted above, in a conventional apparatus, the method is proposed, wherein the wafer is divided circumferentially into a plurality of segments and is turned about its center to sequentially form bumps in each segment, and an air blowing means for floating and turning is therefore used. In this case, however, since the wafer has been heated on the bonding stage and is also cooled down by the air flow for floating, turning, or, pushing it to one side, the resulting rapid temperature change may adversely affect the wafer.
Yet further, when the wafer is floated on air for a turn above the bonding stage, consistently stable wafer turning is needed in order to increase orientation flat detection precision. Depending upon such factors as the wafer material and shape, however, stabilizing wafer turning under specific conditions can be difficult with conventional technology. For example, when the surface roughness on the back side of the wafer exceeds a particular level, such as with quartz and lithium tantalate wafers, the friction coefficient of the back side of the wafer to the bonding stage surface is high and the wafer does not slide easily. This makes it necessary to use a relatively strong air flow, but when the air flow is increased, air flow turbulence is increased. Thus, this makes it even more difficult to stabilize the wafer turning. A relatively strong air flow is also needed to start turning a heavy or large wafer. Increasing the air flow, however, also increases the effect of wafer inertia. This reduces the precision for stopping the wafer at the end of its turn, and thus leads to orientation flat detection error.
With consideration for the aforementioned problems of the related art, an object of the present invention is therefore to provide a bump bonding apparatus and bump formation method achieving a further increase in productivity, a reduction in cost, and an increase in quality when forming electrode bumps directly on a wafer before dicing it.
To achieve the above object, a first aspect of the present invention relates to a bump bonding apparatus for forming bumps by means of a bonding head on a wafer that has been transported onto a bonding stage using a wafer transporting means. In this case, a wafer has been previously regulated for its position so that an orientation flat formed at a circumferential edge of the wafer is oriented in a specific direction. The transporting portion of this bump bonding apparatus comprises an orientation flat detecting means for detecting the location of the orientation flat of the wafer on the bonding stage.
By thus providing the orientation flat detecting means on the transporting portion, the sensor is not subject to the high temperature heat of the bonding stage, which is different from the related art in which the sensor is provided on the bonding stage. It is therefore not necessary to use a particularly high temperature resistant sensor. Furthermore, since the orientation flat detecting means can move in conjunction with movement of the transporting portion, the location of orientation flat detection is not limited to one side of the bonding stage, which is different from the related art in which the sensor is fixed at one side of the bonding stage.
The orientation flat detecting means is preferably an optical sensor having a light emitting element and a receptor element, and is provided on a chucking means of the transporting portion. By using an optical sensor, the position of the orientation flat can be more reliably detected. In addition, by providing the sensor on the chucking means of the wafer transporting portion, the orientation flat, can be detected from above the wafer, or more specifically from above the bonding stage, thereby more reliably avoiding the effects of heat from the bonding stage.
Yet further preferably, there is a plurality of the detecting means arranged in a direction perpendicular to the travel direction of the transporting portion. By thus arranging a plurality of the detecting means perpendicularly to the direction of the transporting means travel, orientation flat detection with even greater precision can be achieved.
Yet further preferably, a bevel with a specific slope is formed in the top surface of the bonding stage at and near the edge of the bonding stage. By thus forming appropriately sloped bevels on the bonding stage, when detecting an orientation flat from above the wafer, a detection light emitted from the detecting means is reflected at the bevel in different directions from that of incidence when the orientation flat is desirably positioned directly below the sensor. More specifically, when the orientation flat is positioned directly below the sensor, the detection beam will not be reflected from the top of the bonding stage back to the receptor, and will thus not interfere with orientation flat detection.
Yet further preferably, a pair of positioning rollers is provided on both right and left sides of the bonding stage. A floating air blower for floating a wafer, a turning air blower for turning a wafer, a first positioning air outlet for pushing a turning wafer to a pair of the positioning rollers on one side and stopping its turn, and a second positioning air outlet for pushing a turning wafer to a pair of the positioning rollers on the other side, are provided on the top surface of the bonding stage. A switching means is also provided for switching the air supply to the first and second regulating air outlets. It is therefore possible to push the wafer to either side of the bonding stage. In this case, since the orientation flat sensor can also move in conjunction with the transporting means, detecting the orientation flat is not limited to only one side of the bonding stage, and the orientation flat can be detected at either side of it.
A bump bonding apparatus according to a second aspect of the present invention forms bumps by means of a bonding head on a wafer supplied to a bonding stage. The apparatus has a pair of positioning rollers disposed on both right and left sides of the bonding stage and has, on the top surface of the bonding stage, a floating air blower for floating a wafer and a turning air blower for turning a wafer, and a positioning air outlet for pushing a turning wafer to a pair of the positioning rollers on at least one side and stopping its turn. The bonding stage comprises a stage plate in which the air outlets are disposed, a heat block disposed below the stage plate, and an air chamber provided in the stage plate. The air chamber leads to each of the air outlets and can temporarily store supply air from outside.
The air chamber in this bump bonding apparatus allows the supply air from outside to warm a certain degree in the air chamber before it is ejected from the air outlets to the bottom of the wafer. Thus, when air is blown from the air outlets against the bottom of the wafer to float, turn, or position a wafer heated on the bonding stage, the temperature gradient of ejected-air cooling of the heated wafer is more gradual than with a conventional bump bonding apparatus. Thus, the effects of wafer cooling by these ejected-air streams can be effectively avoided.
A bump bonding apparatus according to a third aspect of the present invention forms bumps by means of a bonding head on a wafer supplied to a bonding stage. This apparatus has on the top surface of the bonding stage a floating air blower for floating a wafer and a turning air blower for turning a wafer, and the air flow from the turning air blower against a back side of the wafer during wafer turn is variable.
By thus varying the air flow against the backside of the wafer during wafer turn, the air flow can be adjusted according to the wafer material, shape, and size. The air flow can thus be controlled to achieve stable wafer turn.
Yet further preferably, the turning air blower comprises: a plurality of turning air outlets disposed in the substantial same circumference on the top of the bonding stage; an air supply path of which one end leads to the turning air outlets, and the other end branches; a normal turning air supplying means disposed at one branch of the air supply path; and an auxiliary turning air supplying means disposed at another branch of the air supply path and operable in addition to the normal turning air supplying means. Additionally, the air flow to the back side of a wafer from the turning air blower can be changed by controlling the air supplying means to supply air at a specific flow rate. Therefore, it is possible to control the air flow to a specific level at the air supplying means disposed on the opposite end of the air supply path from the plurality of turning air outlets. Thereby, the air flow to the back side of the wafer from the turning air outlets is varied. Air supply can thus be adjusted according to the wafer material, size, and shape to achieve stable wafer turn. It is also possible to smoothly slow wafer turn from high speed to low speed without completely interrupting the air supply because air supplied from both supplying means is ejected from the same air outlets.
Alternatively, the turning air blower comprises: a plurality of turning air outlets disposed on a first circumference on the top of the bonding stage; an auxiliary turning air outlet disposed on a second circumference on the top of the bonding stage; a normal turning air supplying means disposed at the other end of an air supply path of which a first end leads to turning air outlets; and an auxiliary turning air supplying means disposed at the other end of an air supply path of which a first end leads to auxiliary turning air outlets, and which is operable in addition to the normal turning air supplying means. In this case, the air flow to the back side of a wafer from the turning air blower can be changed by controlling the air supplying means to supply air at a specific flow rate. Therefore, it is possible to control the air flow to a specific level at the air supplying means disposed on the opposite end of the air supply path from the plurality of turning air outlets, and thereby vary the air flow to the back side of the wafer from the turning air outlets. Air supply can thus be adjusted according to the wafer material, size, and shape to achieve stable wafer turn.
Yet further preferably, air flow is controllable in the normal turning air blower and/or the auxiliary turning air blower. This enables even more precise control of the air flow from the air outlets, enables air flow to be smoothly changed, and can thus further stabilize wafer turn.
Yet further preferably, the air flow to the backside of the wafer during wafer turn is controllable by supplying air in steps from the auxiliary turning air blower. By thus enabling air flow from the auxiliary turning air blower to be increased in steps at the start of turning, air flow from the air outlets can be smoothly changed, wafer turn can be gradually started, and wafer slipping due to rapid starting can be prevented. Further, the air flow to the backside of the wafer during wafer turn is controllable by intermittently supplying air from the auxiliary turning air blower. By thus intermittently supplying auxiliary air during wafer turn, low speed, stable wafer turn can be maintained even with wafers having a surface roughness on the back side exceeding a particular level that tends to cause the wafer to stop easily on the bonding stage.
Yet further preferably, the air outlets of the turning air blower are disposed on top of the bonding stage on a circumference at or near the wafer edge, or a circumference thereinside. In this case, air for turning the wafer is ejected from the bonding stage, thereby distributing torque across the backside of the wafer and enabling stable wafer turn. This is particularly effective with large wafers.
There is yet further preferably an orientation flat detecting means for detecting the position of a wafer orientation flat on the bonding stage. It is thus possible to detect the position of the orientation flat after the wafer is turned on the bonding stage, and thereby confirm the orientation of the wafer on the bonding stage.
A bump bonding apparatus according to a fourth aspect of the present invention forms bumps by means of a bonding head on a wafer, which has been previously regulated for its position so that an orientation flat formed at a circumferential edge of the wafer is oriented in a specific direction, and has been transported onto a bonding stage by a transporting portion. The transporting portion comprises a chucking means for holding a wafer at six points.
With the 6-points chucking means of the present invention, the wafer will not be shifted off-center even if the chuck holds the wafer with one of the chucking points being on the orientation flat. Thus, offset positioning of the orientation flat can be effectively prevented when a wafer is transported onto the bonding stage, which is different from a 4-points chucking means.
A bump bonding apparatus according to a fifth aspect of the present invention has a loading station having a carrier for storing a plurality of wafers stacked therein with a specific gap therebetween, and a lifter for positioning the carrier at a specific vertical position. This apparatus forms bumps by means of a bonding head on a wafer extracted from the carrier by an extracting means and placed on a bonding stage by means of a transporting means. It further comprises at the loading station: a detecting means for detecting whether an orientation flat of a wafer in the carrier is within a specific range for a reference position, and means for notifying the operator when the detecting means detects the orientation flat to not be within this specific range for the reference position.
The orientation flat detecting means can thus reliably detect whether the wafer is desirably positioned, and the operator can be notified of the result. The operator""s task of inserting wafers into the carrier is thus made easier, the job of adjusting the position of the orientation; flat can be simplified, and the need for manually handling the wafers can be reduced. It is to be noted that the orientation flat detecting means is preferably located at the lifter of the loading station.
Yet further preferably the orientation flat detecting means is a plurality of optical sensors having a light emitting element and a receptor element disposed perpendicularly to the direction of wafer extraction from the carrier. Using optical sensors for the orientation flat detecting means thus assures reliable orientation flat detection, while also simplifying both the detecting means and its mounting structure. Providing a plurality of sensors as described above also enables even higher detection precision.
A bump bonding method according to a sixth aspect of the present invention forms bumps on a wafer supplied to a bonding stage by means of a bonding head. A floating air blower for floating a wafer and a turning air blower for turning a wafer are provided on the bonding stage, and the method comprises a step for variably controlling air flow from the turning air blower to a back side of the wafer during wafer turn.
It is therefore possible to vary the air flow to the back side of the wafer during wafer turn, and thus adjust the air supply according to the wafer material, size, and shape to achieve stable wafer turn.
Yet further preferably, in step for variably controlling air flow from the turning air blower during wafer turn, air from the turning air blower is supplied by stages. By thus increasing turning air flow by stages at the start of the turning, air flow from the air outlets can be smoothly changed, wafer turn can be gradually started, and wafer slipping due to rapid starting can be prevented.
Further alternatively, the air flow to the backside of the wafer during wafer turn can be intermittently supplied from the auxiliary turning air blower. By thus intermittently supplying air during wafer turn, low speed, stable wafer turn can be maintained even with wafers having a surface roughness on the back side exceeding a particular level that tends to cause the wafer to stop easily on the bonding stage.
Yet further preferably, an orientation flat detecting means is provided for detecting the position of the orientation flat of a wafer on the bonding stage after wafer turn. In this case, the position of the orientation flat can be detected after wafer turn to confirm the orientation of the wafer on the bonding stage.
Other objects and attainments together with a fuller understanding of the invention will become apparent and appreciated by referring to the following description and claims taken in conjunction with the accompanying drawings.